306 ANIMAL HEAT. 



These and similar facts point to so close a relation between the 

 intensity of respiration and that of heat-production, that the one of 

 these processes may be taken, in general terms, as the measure of the 

 other ; particularly as respiration consists in the absorption of oxygen 

 and the exhalation of carbonic acid, and as we know that the oxidation 

 of carbonaceous matters, outside the body, is one of the readiest means 

 for the production of heat. 



This connection, however, is not an immediate one, nor can we con- 

 sider the production of heat in the living body as a result of simple 

 oxidation. We have already seen in the preceding chapter that the 

 formation of carbonic acid is not due to direct oxidation, since it will 

 go on in the tissues without the immediate presence of oxygen. Re- 

 spiration is essential to all the phenomena of animal life, and may be 

 taken as the criterion of vital activity in general. The production of 

 heat is one of these phenomena, and, like the rest, increases or dimin- 

 ishes in intensity with that of respiration ; but it cannot be said to 

 depend upon respiration in any peculiar or exclusive manner. 



The Evolution of Heat and the Products of Eespiration not strictly 

 proportional. Furthermore, notwithstanding the general relation in 

 activity between the two functions, if an accurate comparison be made 

 between the quantity of heat produced, under different circumstances, 

 and that of oxygen absorbed or of carbonic acid exhaled, they are 

 found not to correspond exactly with each other. In the experiments 

 of Senator on the bodily temperature in dogs, it was shown that the 

 evolution of heat and the production of carbonic acid do not follow the 

 same rate of increase. They are both augmented during digestion, but 

 the production of carbonic acid never in the same degree with that of 

 heat. An examination of the averages obtained in three series of obser- 

 tions gives the following result : 



XT , ( Fasting . 

 Dog No. 1 { In d]gestioi 



QUANTITIES OF HEAT AND OF CARBONIC ACID PRODUCED BY THE DOG IN ONE HOUR. 



Condition Carbonic acid in Proportion 



of the animal. grammes. Heat units. between the two. 



. . 3.455 12.630 1 to 3.65 



ion . . . 5.013 18.875 1 to 3.76 



( Fasting .... 4405 16.500 1 to 3.72 



Dog No. 2 j In digestion m t m 4837 19 390 1 to 4.01 



f Fasting .... 3.154 16.880 1 to 5.35 



Dog No. 3 1 In digestion , m 3, 846 2 1.960 1 to 5.71 



Thus the proportion of carbonic acid formed to the heat produced is 

 different in the three animals when compared with each other in the 

 same condition ; and it also varies in each animal under the different 

 conditions of fasting and digestion. 



In the experiments of the same observer on the effect exerted by arti- 

 ficial cooling on the animal body, he found that under the influence of a 

 low temperature the actual production of heat in dogs was never in- 

 creased, but was usually perceptibly diminished; while that of carbonic 

 acid was generally somewhat increased and never diminished. 



